1. Field of the Invention
The present invention relates to a micromotion device using a piezoelectric device. The invention also relates to a scanning probe microscope that is a general term for a family of instruments including scanning tunneling microscope, atomic force microscope, magnetic force microscope, friction force microscope, viscoelasticity microscope (VE-AFM), scanning Kelvin probe microscope (SKPM), scanning near field microscope, and other similar instruments.
2. Description of Related Art
In recent years, a scanning probe microscope for obtaining a topographical image, magnetic image, or spectroscopic image of a surface of a sample has attracted attention. In particular, the microscope has a cantilever equipped with a probe. The cantilever is placed opposite to the sample. The distance between the probe and sample is set to nanometers or less. The probe is scanned over the sample surface to measure a physical quantity, such as an interatomic force, magnetic force, or electrostatic force exerted between the probe and sample. The topographical image, magnetic image, or spectroscopic image is derived based on the result of the measurement.
To scan the probe relative to the sample surface, a scanner that is a micromotion device as shown in FIG. 1 is used. In FIG. 1, a mount stage 6 is fitted to an instrument (not shown). One end of a cylindrical or tubular piezoelectric device 1 (also known as a piezo tube) is mounted to the mount stage 6. A probe 2 is installed at the other, free end. FIG. 2 is a cross-sectional view of the micromotion device shown in FIG. 1. In FIG. 2, the mount stage 6 and the piezo tube 1 are held together in a mount portion 8. The stage and piezo tube may also be held together with screws. In scanning probe microscopy requiring atomic resolution, even a low level of rattling is not tolerated. Consequently, they are held together chiefly with adhesive.
The free end of the piezo tube 1 is displaced by deformation caused by a distortion utilizing elongation or contraction of the piezoelectric device under electrodes 3 and 4. The elongation or contraction is produced by applying a voltage to the electrodes 3 and 4. Therefore, large stress is induced in the mount portion 8.
Furthermore, in the case of a scanning probe microscope equipped with an ultra-high vacuum sample chamber, a bakeout is performed to remove gases adhering to the inside of the sample chamber to obtain an ultra-high vacuum environment in the sample chamber where a scanner is installed. In particular, a heating cycle consisting of heating the chamber to a bakeout temperature of about 150° C. from room temperature and returning the temperature from the bakeout temperature to room temperature takes place. The piezo tube 1 has a small coefficient of thermal expansion and is hard and brittle. The metal material of the mount stage 6 has a coefficient of expansion larger than that of the piezoelectric device. Therefore, during the heating cycle, the mount stage 6 varies more greatly than the piezo tube 1. Furthermore, the adhesive that can be used in an ultra-high vacuum environment where little gas is produced shows a small coefficient of thermal expansion after curing and hardly deforms. Hence, the piezo tube 1, adhesive, and the mount stage 6 made of the metal have different coefficients of thermal expansion. As a result, the piezo tube 1 is damaged or the adhesive peels off from the mount portion 8.
Where an observation is made under ultra-high vacuum, low-temperature conditions, the temperature is lowered to the temperature of liquid nitrogen or liquid helium by the refrigerant after the bakeout and, therefore, the components differ more widely in coefficient of thermal expansion. In consequence, if a heating cycle of room temperature-bakeout temperature-room temperature-low temperature-room temperature is performed, the mount portion 8 is more likely to be damaged.
To solve this problem, a prior art technique consisting of inserting a buffer ceramic part between the piezo tube and the metal mount stage has been proposed. However, the buffer ceramic part has a coefficient of thermal expansion close to that of the piezo tube. Consequently, there is the problem that the adhesive peels off between the buffer part and the metal mount stage.
One prior art technique is a micromotion device for driving a microscope probe (see, for example, Japanese patent laid-open No. H7-287022). The micromotion device is made of a cylindrical piezoelectric ceramic device provided with cutouts to prevent electromagnetically induced noise and electrical current interference.
The issue addressed by the present invention is that the piezo tube is damaged due to a difference in thermal deformation between the piezo tube and the mount stage during the heating cycle occurring in the scanning probe microscope or other similar instrument.